In construction, concrete is a composite building material made from the combination of aggregate and cement binder. The most common form of concrete is Portland cement concrete, which consists of mineral aggregate (generally gravel and sand), Portland cement and water. When water is added to the concrete mixture, the cement hydrates, gluing the other components together and eventually creating a stone-like material. When used in the generic sense, this is the material referred to by the term concrete. Concrete is used to make pavements, building structures, foundations, motorways/roads, overpasses, parking structures, and bases for gates/fences/poles. The shortcomings in conventional concrete as a building material are now described.
One problem with concrete is that it is very heavy with respect to its unit volume. Due to this high density, when concrete is used as a building material, additional support is required to compensate for this heavy weight. Thus, some have tried in the past to make lower density concrete (and thus lighter concrete) by placing air/gas bubbles in the concrete. The problem of most methods used to lower density is that such methods also lower strength. That may be acceptable for a wall panel, but not for a support structure. When the density is lower in a structural panel, it is less strong, and thus requires an increased volume of concrete to insure that it is sufficiently supported. Thus, what is needed is a lighter concrete material which retains the strength typically associated with heavier concrete.
Another method used in the past to lower the density of concrete (having a specific gravity of approximately 2.4) has been to use low density aggregates, such as sea shells (having a specific gravity of approximately 1.55), to lower the density of the concrete (and thus lighten the concrete). The combination of concrete with aggregate is referred to herein as “composite concrete”. Aggregate is the component of a composite material used to resist compressive stress. For efficient filling, aggregate should be much smaller than the finished item, but have a wide variety of sizes. The “cementatious portion” of “composite concrete” can be comprised of cement, sand and possibly other additives, such as fly ash. Composite concrete which contains the sea shell aggregate has a lower density (118 lbs/cubic foot (PCF)), as compared to typical concrete (140-150 PCF). The use of sea shells as an aggregate in composite concrete reduces the weight of a structural member by approximately 17%, when the composite concrete is comprised 60 wt % cementation portion (e.g., cement, sand and fly ash), 32.5 wt % sea shell aggregate and 7.5 wt % air. While this composite concrete is useful, it is highly desirable to develop a Composite concrete which has an average density of less than 110 PCF.
Other attempts to lower the density of composite concrete have been made by using other low density aggregates, such as plastics. However, the problem with using these other types of aggregates in composite concrete is that when stressed, the composite concrete will tend to crack along the interface of the aggregates and the cementatious portion. It substantially weakens the resulting product if the boundary is weaker than either phase (aggregate or cementatious portion). This results in a weaker composite concrete. Thus, what is needed is a lower density aggregate that will be strong and adhere to the cementatious portion, so as to form a stronger, lower density composite concrete.
The concept of using foam glass as a construction material is also well known in the prior art. Generally such foam glass has been used as a high temperature insulator and thus seeks to minimize its density and weight and is not used as an aggregate or filler for composite concrete in building materials. The shortcoming in such conventional foam glass as relevant to this long standing problem is now described.
For example, Pittsburgh Corning Corporation (“PCC”) of Pittsburgh, Pa. has developed and marketed a product known as Foam Glas® Insulation Systems, which is described in U.S. Pat. Nos. 3,959,541, 4,119,422, 4,198,224, 4,571,321 and 4,623,585. Since the purpose of this tile is to be used as thermal insulation, it lacks surface strength, and can be dented very easily. Because the Foam Glas® Insulation Systems tile is of relatively low density, e.g., 9.5 PCF, such tiles will easily break when exerted to forces typically asserted on structural members of a building.
Unlike the prior art discussed above, the composite concrete using foam glass aggregate of the present invention can be used like concrete, but has a greater strength per unit weight.
Thus, while the prior art is of interest, the known methods and apparatus of the prior art present several limitations which the present invention seeks to overcome.
In particular, it is an object of the present invention to provide a strong, lower density composite concrete which comprises cementatious portion and foam glass aggregate which can be used as a structural member of a building.
It is a further object of the present invention to make a lightweight aggregate that when used in composite concrete has substantially higher strength to weight ratio than concrete.
It is another object of the present invention to make an aggregate that will not absorb substantial amounts of water from the wet concrete when it is formed.
A still further object of the present invention is to make an aggregate that will form a strong bond with the cementatious portion when formed into a composite concrete.
These and other objects will become apparent from the foregoing description.